labs_title

Caldeira Lab Research:Ocean acidification and ocean carbon cycle

Effect of horizontal grid resolution on simulations of oceanic CFC-11 uptake and direct injection of anthropogenic CO2

M.E. Wickett, K. Caldeira & P.B. Duffy

Simulations of direct CO2 injection and CFC-11 uptake were run in two models with different resolutions to assess the difference in results caused by resolution changes. The results show that an improvement in resolution has minimal effect on quality of results. In fact, in predictions of CFC-11 uptake, the difference between the models was smaller than the difference between results and observation.


Wickett, M.E., K. Caldeira and P.B. Duffy, Effect of horizontal grid resolution on simulations of oceanic CFC-11 uptake and direct injection of anthropogenic CO2 , Journal of Geophysical Research (Oceans) 108,Art. No. 3189, 2003.

Oceanic CO2 remaining in the ocean after 100 years in both models: Fine (right) and coarse (left) models yielded similar results for the amount of carbon dioxide remaining in the ocean 100 years after direct injection.

Volume of the ocean versus pH change: The change in pH observed in the model using fine and coarse resolution is plotted here against the volume of the ocean measured. The results from both resolutions are fairly similar.

Abstract

We simulate direct injection of CO2 and uptake of CFC-11 in a global, three dimensional ocean general circulation model using two model resolutions: a coarse resolution of 4º in longitude by 2º in latitude and a finer resolution of 1º in both longitude and latitude. We assess the impact of resolution on the relative effectiveness of ocean carbon sequestration for four different injection sites: New York at 710 and 3025 m depths and San Francisco at 710m and 3025 m depths. Results show that deep injection is generally effective, with relatively small differences in retention, transport, and fluxes between the two resolutions. Results for the change in ocean pH due to CO2 injection show that resolution does limit the details at sufficiently small scales, with the finer resolution showing greater maximum pH changes. Model predictions of CFC-11 uptake generally have shallower penetration than is seen in observations, and the differences between the model resolutions are much smaller than the differences between either simulation and the observations. There is no persuasive evidence of improvement of large-scale results with globally higher horizontal resolution in these non-eddy-resolving simulations to justify the computational expense. However, when local details are the primary interest, the use of higher resolution may be justified. We suggest that the best approach to improving the results of coarse resolution ocean models is not to globally increase horizontal resolution outside of the eddy resolving regime, but rather to pursue other approaches such as improved numerical methods, better parameterizations of sub-grid-scale processes, better forcing data, or perhaps local resolution increases.